Food allergy more than disagreeable

For more than a decade, the rate of reported food allergies among Americans has steadily risen. A 2009 article, for example, in the journal Pediatrics reported doctor visits for food allergies among children tripled between 1993 and 2006. At least one-third of Americans believe they have at least one food allergy.

Are the numbers accurate? Are more people becoming allergic to foods? A full answer is surprisingly hard to pin down, in large part because there’s no clear agreement on what exactly constitutes a food allergy. A paper published last year in the Journal of the American Medical Association concluded that tests commonly used to help diagnose food allergies are often improperly used or misinterpreted.

We asked Dr. Sheila Crowe, director of research in the division of gastroenterology at the University of California San Diego School of Medicine, to better define the issues.

Q: What’s your definition of a food allergy?

A: In 2009, a national panel of experts defined it as “an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.” This definition is helpful, but it doesn’t differentiate between food hypersensitivity – an immediate reaction to specific foods like peanuts, eggs, milk, soy, fish and shellfish due to IgE antibodies to such foods – and other more chronic food allergic conditions, such as celiac disease in which certain cells of the immune system react to gluten and similar proteins found in wheat, rye, barley and other foods. Another type of immune cell called eosinophils can cause chronic digestive problems due to foods as well. I reserve the term “food allergy” for the first category, which was the recommendation of the expert panel.

Q: How does “food intolerance” differ from an allergy?

A: Food intolerance in the United States is defined as an adverse reaction to food not due to the immune system. One of the most common is lactose intolerance, which results from an inability to digest the sugar found in milk, cream, butter and ice cream. Much of the world experiences this condition because levels of the enzyme that digest milk sugar in our intestines decrease with age.

In contrast, allergy to milk protein can cause an acute immune reaction with a skin rash, swelling of the mouth and asthma, or a more chronic immune response that affects the digestive system. Celiac disease is one form of gluten sensitivity in which the immune system is clearly causing inflammation of the intestine, but the cause of other forms of gluten sensitivity not due to celiac disease is not yet known.

Q: Everybody’s had the experience of eating something that “didn’t agree” with them. When do you know it’s something more serious than a bad case of indigestion? When do you seek medical help?

A: You should seek urgent medical attention when eating leads to swelling, wheezing, shortness of breath, feeling faint and other signs of an acute food allergy.

(The San Diego Gluten-Free Expo will be held at the Scottish Rite Center in Mission Valley Nov. 12, noon to 4 p.m. For more information, visit sdgfexpo.com.)